For gaseous or fluid bodies, such as stars and gas giants, the period of rotation varies from the object's equator to its pole due to a phenomenon called differential rotation. The other type of commonly used 'rotation period' is the object's synodic rotation period (or solar day), which may differ, by a fraction of a rotation or more than one rotation, to accommodate the portion of the object's orbital period around a star or another body during one day.įor solid objects, such as rocky planets and asteroids, the rotation period is a single value.

The first one corresponds to the sidereal rotation period (or sidereal day), i.e., the time that the object takes to complete a full rotation around its axis relative to the background stars ( inertial space).

In astronomy, the rotation period or spin period of a celestial object (e.g., star, gas giant, planet, moon, asteroid) has two definitions. Earth's rotation imaged by Deep Space Climate Observatory, with axis tilt

For the general concept, see Rotation period (physics).